This invention relates to a sintered composite containing rather a high concentration of diamond particles to be used as tool blanks and in wear-resistant applications. It also relates to a method for producing such composite economically.
Metal bonded and polycrystalline types of superabrasive tools are widely employed in the industries, such that diamond or c-BN (cubic boron nitride) particles are distributed in- and bonded by means of metallic phase, or the abrasive particles are immediately joined with each other, by treating under a combined pressure-temperature condition where the superabrasive material is thermodynamically stable.
In the manufacture of such metal bonded tool blanks, it is desirable that the binder material should exhibit a high melting point in order to achieve a good hold of the abrasive particles. However, rather low melting metals with limited mechanical strength only are available for such purposes. High sintering temperatures generally inherent to such high melting metals make it almost impossible to practice the sintering by conventional techniques because the superabrasive material undergoes the unavoidable conversion to the lower pressure polymorphism phase, or graphite in the case of diamond, for example.
On the other hand, it is desirable for wear-resistant uses that the tool working-surface should contain as high a concentration as possible of superabrasive particles of excellent hardness, in order to achieve highest surface hardness available. However, since the binder content decreases with increasing abrasive contents, it becomes difficult to achieve an adequate holding of abrasive particles. Good holding by the matrix is obtained usually at an abrasive concentration, in the working surface layer, of 20 vol. % or less for diamond, for example. While such abrasive contents may be sufficient for achieving an acceptable performance with some types of tools such as wheels and blades, they are not necessarily adequate for cutting tools as well as wear-resistant parts.
On the other hand, a higher diamond concentration of, say, 95 volume % or more may be achievable in the tool working surface of polycrystalline, or immediately joined diamond particles. This technique, however, necessitates an ultrahigh pressure apparatus, which in particular has a reaction chamber of inevitably limited volume and geometry, so there are difficulties in the manufacture of large or blocky articles, in addition to the rather high costs.
Another known type comprises a layer of sintered diamond particles that are joined to the substrate of, usually, cemented tungsten carbide. This is likely to suffer from disintegration at the interface, when subjected to an intense heat during the brazing or use.
Therefore, one of the principal objects of the inventions is to eliminate the above-described problems inherent to the conventional techniques. It is another object to provide a composite product in which an increased concentration of superabrasive particles are contained in the surface layer and held adequately, without risking a separation at the interface. It is another object to provide a tool blank and a wear-resistant material, as well as a method for producing such articles.
The inventors previously developed a novel technique for producing a close structured ceramic composite material on the basis of a combined technique of SHS process and compression, which is known from WO97/11803, for example. The metallic component, which melts under the high temperature during the process, flows in and fills effectively the voids among and around the skeletal structure of in-situ formed ceramics, so a product can be now obtained with good heat-resistance and close structure.
It is known that the SHS process can yield an intense heat over a very limited duration of, say, a few seconds. We found in this relation that the heating conditions provided by SHS process causes, due to such short duration, little deterioration in the mechanical strength of diamond particles contained in the reaction composition. This can be said even when the temperature reaches 2000xc2x0 C. or more, which are high enough to cause ceramics to melt or soften.
The composite of the invention essentially comprises a substrate block, which consists of either ceramic material and metallic material or several metallic materials, and a superabrasive containing body arranged in adjacency and joined to said substrate block, which contains at least 25 but not exceeding 95% by volume superabrasive particles relative to the whole body, and a metallic ingredient which is distributed in the superabrasive containing layer, including the working surface, over through the interface and into the substrate and at a concentration that varies up or down from the level at the working surface continuously and/or in steps.
Such composite can be most effectively realized by placing a first mixture of superabrasive particles and pulverized metal in adjacency with a second mixture that is so composed as to undergo a self propagating high temperature synthesis (SHS) process to yield a ceramic substance, causing to initiate the SHS process in said second mixture and thereby producing a heat such that said metal is molten at least partly to penetrate said second mixture and, thereby providing a gradient in said molten metal concentration over the both mixtures, while a pressure is applied simultaneously under said heat in order to compact the resulting structure.